The present invention relates to the storage of thermal energy for the purpose of buffering energy in between asynchronously operating supply and demand systems for such heat.
A typical asynchronously operating supply and demand system is any system that requires power on a constant or a particularly variable basis during, e.g. twenty-four hours of a day, while the prime source is to be solar energy. The night time demand has to be buffered. Other asynchronous systems are those in which the thermal energy can be developed at a constant rate, but the demand fluctuates, possibly within wide limits. In all such systems in which the demand variations cannot be taken up by supply variations, or in which inherent supply variations may create temporary shortages, a buffer system is required in which energy is temporarily stored to be available whenever needed. It is apparent that the storage should not lead to any significant loss in the energy supplied. A significant loss occurs, for example, if the energy is repeatedly converted. Thus, if the prime source furnishes energy in the form of heat, the storage should involve storing heat directly and in a manner in which the buffering makes the energy available also as heat. Moreover, the conditions of heat storage and extraction from the buffer should take into consideration that the end user may require suppliance of the heat under particular temperature conditions. For example, steam power systems operate best at high temperatures; they pose, however, a practical limit which is about 1,000.degree. F. Thus, the buffer should furnish heat which raises the temperature of the steam to 1,000.degree. F. To our knowledge, an efficient heat buffer which can, in fact, furnish steam at that temperature is not known at this time.
Utilization of phase changes, and particularly utilization of the latent heat of fusion as a "buffer," for establishing particular temperature conditions, is, of course, well known, and goes back to prehistoric times when men learned to take advantage of the constant temperature of melting ice. Since then, the latent heat of fusion has been used in other instances for buffering heat transfer. In spite of the fact, therefore, that the latent heat of fusion is a well known phenomenon for buffering thermal conditions and heat flows, a suitable buffering system, for example, for a solarenergy-steam power system, is not known.